ED Ships vs. RL Rockets

Old Duck

Old Duck
I've got a simple science question for those of you who are experts in this field. In ED, we can "slow burn" our way from a planet's surface into outer space if we're patient enough (not using supercruise). Why can't we do this in real life? Why do our rockets need to reach incredibly high escape velocities, being the hare instead of the turtle?

My assumption is it's a combination of efficiency (it uses less fuel to burn hard and fast over a short period of time than it would to go slow and steady over a long period of time) and the need to reach an orbital velocity. To the latter point, how far does one need to go before you no longer need a high orbital velocity to prevent falling back towards the earth?

Anyway, I was just thinking on these things and wondering why we can't "slow burn" our way to, say, the moon for example. I realize this is grade school science for some of you, so please take it easy on the aerospace virgin that I am :)
 

pzykozomatik

pzykozomatik
We totally could. The commonly mentioned escape velocity of about 11 km/s is the initial velocity you'd need, starting from the surface, to escape earth's gravity without having to add any further energy, meaning the downward acceleration that is gravity wouldn't be able to reduce your speed to a halt in time. If we had an engine that constantly propelled a spaceship upward at let's say 1 m/s (after accounting for gravitational pull and ignoring other effects for the sake of argument), it would eventually leave earth's atmosphere, and be considered "escaped" at the exact point where the current escape velocity has been reduced to 1 m/s due to the distance from earth's center.
 

Sylow

Sylow
pzykozomatik said:
If we had an engine that constantly propelled a spaceship upward at let's say 1 m/s (after accounting for gravitational pull and ignoring other effects for the sake of argument), it would eventually leave earth's atmosphere, and be considered "escaped" at the exact point where the current escape velocity has been reduced to 1 m/s due to the distance from earth's center.
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Kind of that. But every second you are off the ground, you would have to deliver the necessary force to compensate for gravitation plus provide one meter of lift. That's a lot of seconds of burning time. It's kind of you want to carry a heavy crate to the upper floor. You can pick it up, then carry it up and set it down after a minute or two. Or you pick it up, then walk up slowly, one step every few minutes, so you have to hold the crate for half an hour or more. You add the same potential energy to the crate, so the work you do might be the same. But your arms might not feel the same way after either procedure.

It's more efficient to accelerate quickly and thus reduce the time you have to push against gravitation.
 

Bigmaec

Bigmaec
Sylow said:
Kind of that. But every second you are off the ground, you would have to deliver the necessary force to compensate for gravitation plus provide one meter of lift. That's a lot of seconds of burning time. It's kind of you want to carry a heavy crate to the upper floor. You can pick it up, then carry it up and set it down after a minute or two. Or you pick it up, then walk up slowly, one step every few minutes, so you have to hold the crate for half an hour or more. You add the same potential energy to the crate, so the work you do might be the same. But your arms might not feel the same way after either procedure.

It's more efficient to accelerate quickly and thus reduce the time you have to push against gravitation.
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And atmospheric drag. Which is ok on Kerbin, cool on Duna and an arx on Eve.
Whoops, wrong game...
 

pzykozomatik

pzykozomatik
Sylow said:
Kind of that. But every second you are off the ground, you would have to deliver the necessary force to compensate for gravitation plus provide one meter of lift. That's a lot of seconds of burning time. It's kind of you want to carry a heavy crate to the upper floor. You can pick it up, then carry it up and set it down after a minute or two. Or you pick it up, then walk up slowly, one step every few minutes, so you have to hold the crate for half an hour or more. You add the same potential energy to the crate, so the work you do might be the same. But your arms might not feel the same way after either procedure.

It's more efficient to accelerate quickly and thus reduce the time you have to push against gravitation.
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True. And the fact that the rocket needs to accelerate the fuel necessary for the whole trip in addition to its own mass at all times, makes my example even more unfeasible. I just put it there as a thought experiment to demonstrate how it indeed would be possible to reach space at a walking pace in theory. Although there is research ongoing into the possibility of propelling a cone shaped projectile with the help of ground based lasers, which would eliminate most of the fuel from the equation and maybe allow us to put objects into orbit at much lower speeds than rockets need someday.
 

Sylow

Sylow
Bigmaec said:
This, the rocket equation is an arxhole.
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Indeed it is. And i pondered if that should also be worked into my answer. But then i remembered XKCDs blog about the machine gun jetpack. It explains it much better and in a much more amusing way than i ever could. :)

pzykozomatik said:
Although there is research ongoing into the possibility of propelling a cone shaped projectile with the help of ground based lasers, which would eliminate most of the fuel from the equation and maybe allow us to put objects into orbit at much lower speeds than rockets need someday.
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Yea. In the end, purely theoretically, the most efficient way would actually be to follow Jules-Gabriel Verne. Shooting things to space with a cannon. No need to lift any fuel, very short time to work against gravitation. The only "slight" problem, neither humans nor what much else what we can construct would be able to withstand the acceleration forces such a cannon would have to apply to its payload.
 
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Bigmaec

Bigmaec
Old Duck said:
I may need to get this Kerbal program next time it's on sale. I feel the need to test all the new questions this thread has brought to my mind. Does this program display things like fuel consumption rate, force of thrust, atmospheric drag, etc?
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Do it, it's awesome. The only other game in my inventory with 1000+ hours.
It doesn't display all you asked for unmodded, but it has A CAPITAL HEAP of mods.
So everything you want, it's there. Want to get all stats. Mod. Want to fly from earth instead of kerbin? Mod.
Want to fly Falcon 9 Heavy or Starship? Yup, Mod.
Beware though, the learning curve is steep as in Elite, but different.
 

Winterwalker

Winterwalker
Just to go back to the ED example, the fuel passes through a fusion powerplant system before it reaches the engines. Although I'm not 100% sure how this (subatomic reaction) works in the sense of propellants, it's surely going to be quite different from the chemical reaction used to power conventional rockets. We don't - for example - have to carry equivalent liquid oxygen that real world rockets react with hydrogen as an accelerant (and luckliy we don't carry hydrazine either).

 
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askavir

askavir
The need for extremely high speeds is not for "escaping gravity" (you could escape gravity travelling at one centimeter per hour as long as you could maintain thrust) but to achieve orbital speeds (for instance to place a satellite in orbit, or to reach the ISS to deliver cargo) or the accelerate the rocket to the adequate speed for long distance travel before fuel is over (for instance to send a probe to Jupiter, or land a robot on Mars)
 

Stealthie

Stealthie
Arioch said:
Fuel.

Playing Kerbal Space Program does wonders for understanding all this sort of stuff!
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This.

You absolutely could escape a planet's atmosphere at any speed (or, more importantly, rate of acceleration) if you had enough fuel.

It's really all about efficiency.
Fundamentally, you need to generate a certain amount of thrust (always at least more than the weight of your ship) in order to escape a planet's gravity.
Ultimately, it doesn't matter if you do that quickly or slowly.
It is, however, more efficient to generate that thrust quickly (thus consuming fuel and making the spaceship much lighter) so you have a much lighter ship, which requires less thrust, to continue on with your journey.

As somebody from NASA once said, "Once you've escaped Earth's atmosphere, you're half way to anywhere".

If somebody invented a tiny little power-source and Ion thrusters (or whatever) were developed to the point where they could provide, say, 2000lbs of thrust, then we probably could have tiny little one-man spaceships gracefully lifting off and flying up into space.
Until then, it's all about having massive amounts of fuel and engines that can convert all that fuel into thrust as quickly as possible.
 
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